Exemplary embodiments of the present invention relate to a technique of reducing or preventing the deterioration of display quality generated when a plurality of data lines divided into groups are driven.
The related art includes an electro-optical panel that performs display using the electro-optical variation of an electro-optical material, such as liquid crystal, that is applied to a light valve of a projector. That is, in this type of electro-optical panel, liquid crystal is interposed between a pair of substrates. As shown in FIG. 5, a plurality of scanning lines 112 and a plurality of data lines 114 are provided on one of the pair of substrates so as to be orthogonal to each other. In addition, a pair of thin film transistors (hereinafter, referred to as a ‘TFT’) 116 and a pixel electrode 118 is provided corresponding to each intersection of the scanning lines 112 and the data lines 114. A transparent counter electrode (common electrode) 108 to which a constant voltage LCcom is applied, is provided opposite to the pixel electrodes 118 on the other substrate, and for example, a TN type of liquid crystal 105 is interposed between both of the substrates. In this way, a liquid crystal capacitor composed of the pixel electrode 118, the counter electrode 108, and the liquid crystal 105 is formed for every pixel.
Further, although not shown in FIG. 5, alignment films are provided on surfaces of both the substrates facing each other with a liquid crystal layer interposed therebetween. A rubbing process is performed on the alignment films such that liquid crystal molecules can be continuously twisted at an angle of, for example, 90° in the lengthwise direction thereof between both the substrates. In addition, polarizers are respectively provided in the alignment direction on the other surfaces of the substrates opposite to each other.
Furthermore, in order to reduce or prevent the leakage of electric charges from the liquid crystal capacitor, a storage capacitor 119 is formed for every pixel. One end of the storage capacitor 119 is connected to the pixel electrode 118 (a drain of the TFT 116), and the other end thereof is connected to the ground having an electric potential Gnd, which is applied to all pixels in common. In the present exemplary embodiment, the other end of the storage capacitor 119 is connected to the electric potential Gnd, but may have a constant electric potential (for example, a voltage LCcom, a power supply voltage having a high potential of a driving circuit, or a power supply voltage having a low potential on the driving circuit).
When an effective voltage value of the liquid crystal capacitor is zero, light passing between the pixel electrodes 118 and the counter electrode 108 is optically rotated at an angle of about 90° according to the twisted liquid crystal molecules. On the other hand, when the effective voltage value is large, the liquid crystal molecules are inclined in the electric potential direction, resulting in the removal of the optical rotation. Therefore, for example, in a transmissive liquid crystal display device, in the case of a normally white mode in which polarizers whose polarizing axes are arranged orthogonal to each other along the alignment direction are respectively provided on the light incident side and the rear side opposite thereto, when the effective voltage value is zero, white display is performed since light passes through the polarizers (transmittance is high). On the other hand, when the effective voltage value is large, the amount of light passing through them is reduced, so that black display is performed (transmittance is low). Thus, when the scanning lines 112 are selected one by one to turn on the TFTs 116, the image signal having the voltage corresponding to the grayscale (or brightness) of the pixel can be applied to the pixel electrode 118 through the data line 114, and thus it is possible to control the effective voltage value of the liquid crystal capacitor for each pixel. This control enables predetermined display.
Of course, the projector to which the electro-optical panel is applied does not have a function to form an image in itself, but receives image data (or image signals) from a host apparatus, such as a personal computer or a television tuner, to form an image. Since the image data is supplied in the manner of horizontally and vertically scanning pixels arranged in a matrix, it is appropriate to drive the electro-optical panel used for the projector according to this manner. Therefore, a point-sequential driving method is employed for the electro-optical panel used for the projector as a driving method to supply image signals to the data lines 114. In the point-sequential driving method, the image data are converted into image signals suitable for driving liquid crystal, and the image signals are sampled and supplied to the respective data lines 114 in the period where one scanning line 112 is selected (one effective horizontal scanning period).
Further, in recent years, a high-definition display device has strongly been demanded. The high definition can be addressed or achieved by increasing the number of scanning lines 12 and the number of data lines 114. However, in this case, one horizontal scanning period is shortened with an increase in the number of scanning lines 112, and in a point-sequential method, sampling time on the data line 114 is shortened with an increase of the number of data lines 114.
In the point-sequential method, with the progress of the high definition, since the time when image signals are sampled to the data lines 114 is not sufficiently secured, an electro-optical panel 100 is driven by a so-called phase expansion driving method. In the phase expansion driving method, the data lines 114 are divided into a plurality of blocks each composed of predetermined data lines (in this case, six data lines). In addition, image signals are distributed into six channels (phases) corresponding to the number of data line 114 included in one block and extend six times along a time axis, so that the distributed image signals are supplied to image signal lines 171 as image signals Vid1 to Vid6.
Meanwhile, in FIG. 5, a drain of an N-channel TFT 151, serving as a sampling switch, is connected to one end of the leftmost data line 114 among six data lines 114 belonging to an i-th column block (where i is one of integers 1, 2, . . . , n) from the left side, and a source thereof is connected to the image signal line 171 to which the image signal Vid1 is supplied. Similarly, a drain of the corresponding TFT 151 is connected to one end of each of the second column, third column, . . . , sixth column data lines 114 in the i-th block from the left side, and a source thereof is connected to each of the image signal lines 171 to which the image signals Vid2, Vid3, . . . , Vid6 are respectively supplied.
Further, in the structure shown in FIG. 5, when the total number of the scanning lines 112 is ‘m’ and the total number of the data line 114 is ‘6n’ (where m and n both are integers), pixels are arranged in a matrix of m rows by 6n columns corresponding to intersections of the scanning lines 112 and the data lines 114.
Furthermore, as described below, the image signals Vid1 to Vid6 may be called channels ch1 to ch6. In this case, since the data line 114 belonging to a block corresponds to any one of seven image signal lines 171, for example, the leftmost data line 114 in a certain block correspond to the channel ch1.
Next, as shown in FIG. 6, a scanning line driving circuit 130 shifts a start pulse DY supplied at the beginning of the vertical scanning period according to a clock signal CLY to output scanning signals G1, G2, G3, . . . , Gm which sequentially exclusively turn to H levels. In addition, as shown in FIG. 6, a shift register 140 shifts a start pulse DX supplied at the beginning of the horizontal scanning period according to a clock signal CLX to output sampling signals S1, S2, S3, . . . , Sn which sequentially exclusively turn to H levels. Further, the pulse width of each of the sampling signals S1, S2, S3, . . . , Sn which turn to the H levels is narrowed up to a period Smp in which the pulse width is narrower than a half the period of the clock signal CLX such that adjacent sampling signals do not overlap each other.
In the phase expansion driving method, the respective blocks are selected one by one in one horizontal scanning period by the sampling signals S1, S2, S3, . . . , Sn. Here, for example, when an i-th block is selected and a sampling signal Si becomes an H level, six TFTs 151 whose drains are connected to the data lines 114 belonging to the block are simultaneously turned on. Therefore, the image signals Vid1, Vid2, Vid3, . . . , Vid6 are sampled to the first column, second column, third column, . . . , sixth column data lines 114 belonging to the block, respectively, and are then written on pixel electrodes 108 of the pixels corresponding to the intersections of the selected scanning line and the six data lines belonging to the i-th block, respectively.
In the phase expansion driving method, the time required for sampling can be lengthened six times longer than the structure in which the data lines 114 are selected one by one, to sample the image signals. Therefore, as described above, this method is suitable for addressing or achieving a high-definition display. In addition, here, the number of data lines belonging to one block is ‘6’, but the number of data lines is not limited thereto.
However, in the phase expansion driving method, a plurality of data lines 114 divided into blocks each composed of predetermined data lines are driven, which causes a phenomenon (block ghost) in which display contents of a certain block displayed on pixels in an adjacent block, overlapped with the display contents of the adjacent block. The inventors suggested a technique in which the correction amount of the grayscale of pixels belonging to a target block is calculated based on the average variation of pixels belonging to the block positioned one block ahead of the target block, and in which the correction amount is added to image data to be supplied to the pixels belonging to the target block to remove the block ghost. See related art document Japanese Unexamined Patent Application Publication No. 2002-149136.
However, according the technique described in related art document Japanese Unexamined Patent Application Publication No. 2002-149136, the block ghost is suppressed to some degree, but the block ghost as much as can be viewed, still occurs. Exemplary embodiments of the present invention are designed to address or solve the above-mentioned and/or other problems. It is an object of exemplary embodiments of the invention to provide an image signal correcting method, a correcting circuit, and an electro-optical device, capable of reducing or preventing the generation of the block ghost and of displaying a high-quality image, and to provide an electronic apparatus having the electro-optical device as a display unit.